The present invention relates to aerodynamic rotors and, more particularly, to the tail rotor and blade of a helicopter.
Aerodynamic rotors of the kind of interest for helicopters are comprised of a rotatably driven anvil and an aerodynamic blade. When such rotors are driven under load, the blades are subjected to substantial stress caused by flat-wise loading which results in a substantial increase in the head moment of the driven anvil and in the blade material.
In particular, with respect to tail rotors of helicopters, for simplicity of construction, increased reliability, and reduced maintenance cost, it is desirable that a non-articulated blade be clamped between two hub plates forming an anvil with the blade acting as a cantilevered beam upon flat-wise flapping or bending due to flat-wise flexure forces generated under load. However, such a construction would result in an increase in the head moments of the anvil of approximately three times greater than those of semi-articulated rotors which are commonly used. Such higher head moments would necessitate redesign of the tail gear output shaft, tail gear box support fitting, major components of the tail gear box and possibly the tail pylon structure. Accordingly, it is desirable to avoid such a major redesign and increased weight.
In order to reduce the increased stresses which result, prior anvil designs were provided with configured bearing areas engagable by the blade during flapping for permitting sufficient bearing support of the blade at the hub while permitting some movement of the blade in the hub area for reducing the high hub moment which results. However, even in this case, severe stress/strain is produced within the blade and there still are severe fatique life limitations on the blade and rotor head with the requirement for heavier hub components having undesirable excess weight.
Accordingly, it is desirable to provide an aerodynamic rotor having improved reliability and maintenance with reduced internal blade stress/strain and reduced head moment forces generated during flat-wise loading of the rotor.